1. Field of the Invention
The invention relates in general to valves for the control of fluid flow. More particularly, the invention relates to fluid control valves for use in zinc-air batteries.
2. Description of the Related Art
Electrochemical cells are used for electrically powering portable and mobile devices. Typically these are ganged together to form batteries that provide from 3 to 15 volts. Examples are lead-acid batteries in automotive applications, nickel-cadmium batteries used to power hand-held devices such as electric flashlights, and lithium batteries used in lap-top computers, cameras and cell phones.
Another type of electrochemical cell is that of a zinc-air battery which is activated when air as the fluid enters the cell. A typical zinc-air battery cell is comprised of an electrolyte, such as an alkali hydroxide in a 20–40% weight solution with water. The battery acts as a partial fuel cell because it uses oxygen from air as the cathode. Oxygen is let into the battery and is reduced on a carbon surface. The cathode undergoes the electrochemical reaction ½ O2+H2O+2e=2 OH−. The anode is zinc which undergoes the reaction Zn2++2 OH−=Zn(OH)2. The overall reaction is 2 Zn+O2+2 H2O=2 Zn(OH)2 which produces an electrical potential or voltage.
The electrical potential produced by the cell can drive a current to a load in an electrical circuit. The cell reactions, and therefore the current, terminate when the cell is isolated from the oxygen source.
Each battery technology has advantages and disadvantages. One method of comparing batteries is to rank them by cost versus weight per watt-hour of energy storage. By these criteria, zinc-air batteries can out-perform existing technologies as well as the majority of other technologies that are planned for development.
One feature of zinc-air batteries has inhibited their development. Existing electrochemical cells become saturated under conditions of no load so that during periods of non-use the energy content is preserved or lost only gradually. Thus the shelf life of such a cell is reasonably long. The oxidation process in zinc-air cells however continues as long as the electrode is exposed to oxygen, so the shelf life of the battery is severely reduced. It would be desirable to provide a fluid flow control valve in electrochemical cell of a size which is sufficiently small for use in electrically powering portable and mobile devices with long shelf life.
The need has therefore been recognized for a fluid control valve for electrochemical cells which obviates the foregoing and other limitations and disadvantages of prior art fluid control valves. Despite the various fluid control valve in the prior art, there has heretofore not been provided a suitable and attractive solution to these problems.